1. Field of the Invention
The present invention relates to the medical arts, and in particular, to targeted liposomal drug delivery.
2. Discussion of the Related Art
Myeloid dendritic cells (My-DCs) belong to the most potent group of professional antigen-presenting cells, with the unique ability to induce primary cellular and humoral immune responses (reviewed in Banchereau J, Paczesny S, Blanco P, Bennett L, Pascual V, Fay J, Palucka A K, Dendritic cells: controllers of the immune system and a new promise for immunotherapy, Ann N.Y. Acad Sci 987:180-7 [2003]). These cells, within the lymphoid organs and structures, are also an important component of the HIV reservoir, together with other major sanctuary populations, i.e. follicular dendritic cells, macrophages, resting/memory T cells, and cells within the central nervous system. (E.g., Schrager L K, D'Souza M P, Cellular and anatomical reservoirs of HIV-I in patients receiving potent antiretroviral combination therapy, JAMA 280:67-71 [1998]). It is a key characteristic of reservoir cells that they are compromised and exploited, but not killed, by HIV, thus leading to a continuous infection of other immune and non-immune cells within an infected person. (Gieseler R K, Marquitan G, Scolaro M J, Cohen M D, Lessons from history: dysfunctional APCs, inherent dangers of STI and an important goal, as yet unmet, Trends Immunol. 2003; 24:11).
In-vitro generation of My-DCs has enabled comprehensive phenotypic and functional characterization of the My-DCs and the study of the ontogeny of these cells, which have been found to share with macrophages an early common myeloid progenitor (Gieseler R K, Röber R A, Kuhn R, Weber K, Osborn M, Peters J H, Dendritic accessory cells derived from rat bone marrow precursors under chemically defined conditions in vitro belong to the myeloid lineage, Eur J Cell Biol 1991; 54:171-81; Peters J H, Xu H, Ruppert J, Ostermeier D, Friedrichs D, Gieseler R K, Signals required for differentiating dendritic cells from human monocytes in vitro, Adv Exp Med Biol 1993; 329:275-80; Peters J H, Gieseler R, Thiele B, Steinbach F, Dendritic cells: from ontogenetic orphans to myelomonocytic descendants, Immunol Today 1996; 17:273-8; Gieseler R, Heise D, Soruri A, Schwartz P, Peters J H, In-vitro differentiation of mature dendritic cells from human blood monocytes, Dev Immunol 1998; 6:25-39).
The discovery of the My-DC-specific intercellular adhesion molecule 3-grabbing nonintegrin (DC-SIGN) in the year 2000 was a milestone of immunologic research: DC-SIGN, one of several C-type lectins, is both a distinctive key DC molecule and plays an essential role in the capture and migratory transport of HIV. Besides T-cell infection due to active virus production by My-DCs, interaction of HIV and DC-SIGN eventually enables My-DCs to infect in-trans cooperating T-helper cells. Also, variants of DC-SIGN are expressed by macrophages (another major HIV-1 reservoir), as well as by several mucosal and placental cell types (Soilleux, E J et al. Constitutive and induced expression of DC-SIGN on dendritic cell and macrophage subpopulations in situ and in vitro, J Leukoc Biol 71:445-57 [2002]; Geijtenbeek, T B H et al., Marginal zone macrophages express a murine homologue of DC-SIGN that captures blood-borne antigens in vivo, Blood 100:2908-16 [2002]; Soilleux E J et al., Placental expression of DC-SIGN may mediate intrauterine vertical transmission of HIV, J Pathol. 195(5):586-92 [2001]; Soilleux E J, Coleman N, Transplacental transmission of HIV: a potential role for HIV binding lectins, Int J Biochem Cell Biol.; 35(3):283-7 [2003]; Kammerer U et al., Unique appearance of proliferating antigen-presenting cells expressing DC-SIGN (CD209) in the decidua of early human pregnancy, Am J Pathol. 162(3):887-96 [2003]). These C-type lectins, therefore, qualify as major players in the horizontal and vertical transmission of HIV within a given individual (Geijtenbeek T B, van Kooyk Y, DC-SIGN: a novel HIV receptor on DCs that mediates HIV-1 transmission, Curr Top Microbiol Immunol 276:31-54 [2003]). In vivo, DC-SIGN is not only expressed by myeloid DCs, but also by subpopulations of macrophages, which are another main group of HIV reservoir cells (Soilleux E J et al., Constitutive and induced expression of DC-SIGN on dendritic cell and macrophage subpopulations in situ and in vitro, J Leukoc Biol. 71(3):445-57 [2002]).
It is known that DC-SIGN is an endocytic adhesion receptor.
First, DC-SIGN-attached particles are shuttled into the MHC class II antigen processing and presentation pathway and are accessed to the mechanism generating T-cell immunity (as desirable in case of any viral infection), as well as B-cell immunity (as supportive in the clearance of virus, by mechanisms secondary to the generation of antibodies, such as Fc receptor-mediated phagocytosis or, in case of cytotoxic antibodies, complement-mediated lysis) (e.g., Schjetne K W et al., Mouse C specific T cell clone indicates that DC-SIGN is an efficient target for antibody-mediated delivery of T cell epitopes for MHC class II presentation, lift Immunol 14(12):1423-30 [2002]; Engering, A et al., The dendritic cell-specific adhesion receptor DC-SIGN internalizes antigen for presentation to T cells, J Immunol 168(5):2118-26 [2002]).
Second, Turville et al., demonstrated that Th-cell infection by MyDCs with HIV-1 is a two-phased process that depends on the DCs' developmental stage, including both directional transport of virus to the immunological synapse, as well as active de-novo synthesis of HIV-1 from proviral DNA (Turville S G, Santos J J, Frank I et al. Immunodeficiency virus uptake, turnover, and two-phase transfer in human dendritic cells, Blood; online publication ahead of print: DOI 10.1182/blood-2003-09-3129 [2003]). In addition, the important roles of DC-SIGN in the migratory transport of virus by MyDCs (Geijtenbeek T B H, van Kooyk Y, DC-SIGN: a novel HIV receptor on DCs that mediates HIV-1 transmission, Curr Top Microbiol Immunol; 276:31-54 [2003]) and in the in trans infection of Th cells (Geijtenbeek T B H, Kwon D S, Torensma R et al. DC-SIGN a dendritic cell-specific HIV-1-binding protein that enhances trans-infection of T cells, Cell; 100:587-97 [2000]) very much support a pathogenetic key role for these cells. Intriguingly, it has now been shown that passive transfer from MyDCs to Th cells via DC-SIGN requires that HIV-1 is first internalized into intracellular trypsin-resistant compartments (McDonald D, Wu L, Bohks S M, KewalRamani V N, Unutmaz D, Hope T J, Recruitment of HIV and its receptors to dendritic cell-T cell junctions, Science; 300:1295-7[2003]; Kwon D S, Gregorio G, Bitton N, Hendrickson W A, Littman D R, DC-SIGN-mediated internalization of HIV is required for trans-enhancement of T cell infection, Immunity; 16:135-44 [2002]). Indeed, after infection with HIV-1, intracytoplasmic compartments with accumulated infectious virus are demonstrable in both immature and mature MyDCs (Frank I, Piatak M Jr, Stoessel H, Romani N, Bonnyay D, Lifson J D, Pope M, Infectious and whole inactivated simian immunodeficiency viruses interact similarly with primate dendritic cells (DCs): differential intracellular fate of virions in mature and immature DCs, J Virol; 76:2936-51 [2002]).
Highly Active Antiretroviral Therapy (HAART) has been shown to be effective to reduce the plasma viral load to undetectable levels in HIV-infected individuals and to markedly diminish the number of HIV-1 RNA copies in secondary lymphoid tissues (Wong, J. K. et al., Recovery of replication-competent HIV despite prolonged suppression of plasma viremia, Science, 278:1291-1295 [1997]; Cavert, W. et al., Kinetics of response in lymphoid tissues to antiretroviral therapy of HIV-1 infection, Science 276(5314):960-964 [1997]). However, the capacity of HIV-1 to establish latent infection allows viral particles to persist in tissues despite immune responses and antiretroviral therapy (Gangne J-F, Desormeaux A, Perron S, Tremblay M. J, Bergeron M. G, Targeted delivery of indinavir to HIV-1 primary reservoirs with immunoliposomes, Biochim Biophys Acta, 1558: 198-210 [2002]). It is hypothesized that the susceptibility of dendritic cells to being infected with HIV, together with their crucial immunologic function, leads to the continuous spread of HIV. Therefore, it has been suggested that targeting of anti-virals to these reservoir cells is an important goal to achieve permanent reconstitution of adaptive immunity (Gieseler R K, Marquitan G, Scolaro M J, Cohen M D, Lessons from history: dysfunctional APCs, inherent dangers of STI and an important goal, as yet unmet, Trends Immunol 24:11 [2003]).
Liposomes are a suitable vehicle for specifically delivering encapsulated compounds to any given cell type, provided the existence of an appropriate targeting structure. Because of its highly restricted cellular expression, DC-SIGN qualifies as such a targeting molecule. We have earlier shown inhibition of HIV propagation in infected peripheral blood mononuclear leukocytes after liposomal delivery of sense DNA directed towards the HIV 5′ tat splice acceptor site (Sullivan S M, Gieseler R K, Lenzner S, Ruppert J, Gabrysiak T G, Peters J H, Cox G, Richer L, Martin W J, Scolaro M J, Inhibition of human immunodeficiency virus-1 proliferation by liposome-encapsulated sense DNA to the 5′ tat splice acceptor site, Antisense Res Dev; 2:187-97 [1992]).
Since the discovery in the 1960s that hydration of dry lipid film forms enclosed spherical vesicles or liposomes that resemble miniature cellular organelles with lipid bilayers, the potential use of lipid-drug complexes as biodegradable or biocompatible drug carriers to enhance the potency and reduce the toxicity of therapeutics was recognized (e.g., Bangham A D, Liposomes: the Babraham connection, Chem Phys Lipids 64:275-285 [1993]). Lipid-drug complexes have long been seen as a potential way to improve the Therapeutic Index (TI) of drugs by increasing their localization to specific organs, tissues or cells. The TI is the ratio between the median toxic dose (TD50) and the median effective dose (ED50) of a particular drug. However, application of lipid-drug complexes to drug delivery systems was not realized until 30 years later. Only then were the first series of liposome-based therapeutics approved for human use by the U.S. Food and Drug Administration (FDA). Liposomes have been used as drug carriers in pharmaceutical applications since the mid-1990s (Lian, T. and Ho, R. J. Y., Trends and Developments in Liposome Drug Delivery Systems, J. Pharm. Sci. 90(6):667-80 [2001]).
Although the lipid constituent can vary, many formulations use synthetic products of natural phospholipid, mainly phosphatidylcholine. Most of the liposome formulations approved for human use contain phosphatidylcholine (neutral charge), with fatty acyl chains of varying lengths and degrees of saturation, as a major membrane building block. A fraction of cholesterol (˜30 mol %) is often included in the lipid formulation to modulate rigidity and to reduce serum-induced instability caused by the binding of serum proteins to the liposome membrane.
Based on the head group composition of the lipid and the pH, liposomes can bear a negative, neutral, or positive charge on their surface. The nature and density of charge on the surface of the liposomes influences stability, kinetics, and extent of biodistribution, as well as interaction with and uptake of liposomes by target cells. Liposomes with a neutral surface charge have a lower tendency to be cleared by cells of the reticuloendothelial system (RES) after systemic administration and the highest tendency to aggregate. Although negatively charged liposomes reduce aggregation and have increased stability in suspension, their nonspecific cellular uptake is increased in vivo. Negatively charged liposomes containing phosphatidylserine (PS) or phosphatidylglycerol (PG) were observed to be endocytosed at a faster rate and to a greater extent than neutral liposomes (Allen T M, et al., Liposomes containing synthetic lipid derivatives of poly(ethylene glycol) show prolonged circulation half-lives in vivo, Biochim Biophys Acta 1066:29-36 [1991]; Lee R J, et al., Folate-mediated tumor cell targeting of liposome-entrapped doxorubicin in vitro, Biochim Biophys. Acta 1233:134-144). Negative surface charge is recognized by a variety of receptors on various cell types, including macrophages (Allen T M et al. [1991]; Lee R J, et al., Delivery of liposomes into cultured KB cells via folate receptor-mediated endocytosis, J Biol Chem 269:3198-3204 [1994]).
Inclusion of some glycolipids, such as the ganglioside GM1 or phosphotidylinositol (PI), inhibits uptake by macrophages and RES cells and results in longer circulation times. It has been suggested that a small amount of negatively charged lipids stabilize neutral liposomes against an aggregation-dependent uptake mechanism (Drummond D C, et al., Optimizing liposomes for delivery of chemotherapeutic agents to solid tumors, Pharmacol Rev 51:691-743 [1999]). Positively charged (i.e. cationic) liposomes, often used as a DNA condensation reagent for intracellular DNA delivery in gene therapy, have a high tendency to interact with serum proteins; this interaction results in enhanced uptake by the RES and eventual clearance by lung, liver, or spleen. This mechanism of RES clearance partly explains the low in vivo transfection efficiency. Other factors, including DNA instability, immune-mediated clearance, inflammatory response, and tissue accessibility can also contribute to low transfection efficiency in animals. In fact, high doses of positively charged liposomes have been shown to produce varying degrees of tissue inflammation (Scheule R K, et al., Basis of pulmonary toxicity associated with cationic lipid-mediated gene transfer to the mammalian lung, Hum Gene Ther 8:689-707 [1997]).
The surface of the liposome membrane can be modified to reduce aggregation and avoid recognition by the RES using hydrophilic polymers. This strategy is often referred to as surface hydration or steric modification. Surface modification is often done by incorporating gangliosides, such as GM1, or lipids that are chemically conjugated to hygroscopic or hydrophilic polymers, usually polyethyleneglycol (PEG). This technology is similar to protein PEGylation. Instead of conjugating PEG to therapeutic proteins such as adenosine deaminase (Alderase, for treatment of severe combined immunodeficiency syndrome) to reduce immune recognition and rapid clearance (Beauchamp C, et al., Properties of a novel PEG derivative of calf adenosine deaminase, Adv Exp Med Biol 165:47-52 [1984]), PEG is conjugated to the terminal amine of phosphatidylethanolamine. This added presence of hydrophilic polymers on the liposome membrane surface provides an additional surface hydration layer (Torchilin V P, Immunoliposomes and PEGylated immunoliposornes: possible use of targeted delivery of imaging agents, Immunomethods 4:244-258). The resulting liposomes can be recognized neither by macrophages nor the RES as foreign particles, and thus escape phagocytic clearance. A number of systematic studies have determined the optimum size of PEG polymer and the density of the respective polymeric PEG lipid in the liposome membrane.
Early research has demonstrated that the liposome size affects vesicle distribution and clearance after systemic administration. The rate of liposome uptake by RES increases with the size of the vesicles (Hwang K, Liposome pharmacokinetics, In: Ostro M J, editor, Liposomes: from biophysics to therapeutics, New York: Marcel Dekker, pp. 109-156 [1987]). Whereas RES uptake in vivo can be saturated at high doses of liposomes or by predosing with large quantities of control liposomes, this strategy may not be practical for human use because of the adverse effects related to sustained impairment of physiological functions of the RES. The general trend for liposomes of similar composition is that an increasing size results in enhanced uptake by the RES (Senior J, et al., Tissue distribution of liposomes exhibiting long half-lives in the circulation after intravenous injection, Biochim Biophys Acta 839:1-8 [1985]). Most recent investigations have used unilamellar vesicles, 50-100 nm in size, for systemic drug delivery applications. For example, the antifungal liposome product AmBisome is formulated to the size specification of 45-80 nm to reduce RES uptake. Serum protein binding is an important factor that affects liposome size and increases the rate of clearance in vivo. Complement activation by liposomes and opsonization depend on the size of the liposomes (Devine D V, et al., Liposome-complement interactions in rat serum: Implications for liposome survival studies, Biochim Biophys Acta 1191:43-51 [1994]; Liu D, et al., Recognition and clearance of liposomes containing phosphatidylserine are mediated by serum opsonin, Biochim Biophys Acta 1235:140-146 [1995]). Even with the inclusion of PEG in the liposome compositions to reduce serum protein binding to liposomes, the upper size limit of long-circulation PEG-PE liposomes is ˜200 nm. Due to biological constraints, development of long circulating large (>500 nm) liposomes using steric stabilization methods has not been successful. Hence, considerations of liposome size and its control in manufacturing at an early stage of drug development provide a means to optimize efficiency of liposome drug delivery systems.
The exact mechanisms of biodistribution and disposition in vivo vary depending on the lipid composition, size, charge, and degree of surface hydration/steric hindrance. In addition, the route of administration may also influence the in vivo disposition of liposomes. Immediately after intravenous administration, liposomes are usually coated with serum proteins and taken up by cells of the RES and eventually eliminated. (Chonn A, et al., Association of blood proteins with large unilamellar liposomes in vivo. Relation to circulation lifetimes, J Biol Chem 267:18759-18765 [1992]; Rao M, et al., Delivery of lipids and liposomal proteins to the cytoplasm and Golgi of antigen presenting cells, Adv Drug Deify Rev 41:171-188 [2000]). Plasma proteins that can interact with liposomes include albumin, lipoproteins (i.e., high-density lipoprotein [HDL], low-density lipoprotein [LDL], etc.) and cell-associated proteins. Some of these proteins (e.g., HDL) can remove phospholipids from the liposome bilayer, thereby destabilizing the liposomes. This process may potentially lead to a premature leakage or dissociation of drugs from liposomes.
One of the key properties that make liposomes an invaluable drug delivery system is their ability to modulate the pharmacokinetics of liposome-associated and encapsulated drugs (Hwang K J, Padki M M, Chow D D, Essien H E, Lai J Y, Beaumier P L, Uptake of small liposomes by non-reticuloendothelial tissues, Biochim Biophys Acta; 901(1):88-96 [1987]; Allen T M, Hansen C, Martin F, Redemann C, Yau-Young A, Liposomes containing synthetic lipid derivatives of polyethylene glycol) show prolonged circulation half-lives in vivo, Biochim Biophys Acta; 1066(1):29-36 [1991]; Allen T M, Austin G A, Chonn A, Lin L, Lee K C, Uptake of liposomes by cultured mouse bone marrow macrophages: influence of liposome composition and size, Biochim Biophys Acta; 1061(1):56-64 [1991]; Hwang, K. [1987]; Allen T, et al., Pharmacokinetics of long-circulating liposomes, Adv Drug Del Rev 16:267-284 [1995]). Relative to the same drugs in aqueous solution, significant changes in absorption, biodistribution, and clearance of liposome-associated drug are apparent, resulting in dramatic effects on both the efficacy and toxicity of the entrapped compound (Gabizon A, Liposome circulation time and tumor targeting: implications for cancer chemotherapy, Adv Drug Del Rev 16:285-294 [1995]; Bethune C, et al., Lipid association increases the potency against primary medulloblastoma cells and systemic exposure of 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea (CCNU) in rats, Pharm Res 16:896-903 [1999]). However, therapeutic applications of systemically administered liposomes have been limited by their rapid clearance from the bloodstream and their uptake by the RES (Alving C, et al., Complement-dependent phagocytosis of liposomes: suppression by ‘stealth’ lipids, J Liposome Res 2:383-395 [1992]).
As already mentioned, circulation time can be increased by reducing the liposomesize and modifying the surface/steric effect with PEG derivatives. Also, liposomes with membranes engineered for sufficient stability escaping clearance by the RES are now available. Therefore, long-circulation liposomes that also significantly reduce toxicological profiles of the respective drugs can be used to maintain and extend plasma drug levels. Even though only a small fraction of liposomes eventually accumulate at target sites, prolonged circulation can indirectly enhance accumulation of liposome-associated drugs to targeted tissues.
It is a desideratum to actively enhance targeting of liposomes so as to direct them to the cell populations of interest before substantial clearance by the RES occurs. For example, immunoliposomes have been employed to target the erythrocyte reservoirs of intracellular malarial parasites (Owais, M. et al., Chloroquine encapsulated in malaria-infected erythrocyte-specific antibody-bearing liposomes effectively controls chloroquine-resistant Plasmodium berghei infections in mice, Antimicrob Agents Chemother 39(1):180-4 [1995]; Singh, A M et al., Use of specific polyclonal antibodies for site specific drug targeting to malaria infected erythrocytes in vivo, Indian J Biochem Biophys 30(6):411-3 [1993]).
It is also a desideratum to apply lipid-drug delivery systems to the fight against the HIV/AIDS pandemic. More than 42 million people are estimated to be currently living with HIV/AIDS (UNAIDS [2002; 2003]). This global figure has been projected to increase considerably if no improved means of keeping this infection at bay will be developed and introduced to the global community (Morens D M, Folkers G K, Fauci A S, The challenge of emerging and re-emerging infectious diseases, Nature; 430:242-9 [2004]).
Anti-HIV drugs, such as nucleoside analogs (e.g., dideoxynucleoside derivatives, including 3′-azido-3′-deoxythymidine [AZT], ddC, and ddI), protease inhibitors, or phosphonoacids (e.g., phosphonoformic and phosphonoacetic acids), have previously been lipid-derivatized or incorporated into liposomes (e.g., Hostetler, K Y et al., Methods of treating viral infections using antiviral liponucleotides, Ser. No. 09/846,398, US 2001/0033862; U.S. Pat. No. 5,223,263; Hostetler, K Y et al., Lipid derivatives of phosphonoacids for liposornal incorporation and method of use, U.S. Pat. No. 5,194,654; Gagne I F et al., Targeted delivery of indinavir to HIV-1 primary reservoirs with immunoliposomes, Biochim Biophys Acta 1558(2):198-210 [Feb. 2002]). Still, in one report, subcutaneous injection of liposome-encapsulated ddI to C57BL/6 mice, resulted in low accumulation of liposomes in lymph nodes, compared to intravenous injection (Harvie, P et al., Lymphoid tissues targeting of liposome-encapsulated 2′,3′-dideoxylnosine, AIDS 9(7):701-7 [1995]).
The use of specific vector molecules coupled to, or embedded within, a liposome surface, has been described for enhanced transmembrane delivery and uptake of liposome-encapsulated compounds that otherwise are only insufficiently delivered into a cell, or that are not efficiently delivered to a specifically desirable intracellular organelle (reviewed in: Torchilin V P, Lukyanov A N, Peptide and protein drug delivery to and into tumors: challenges and solutions, Drug Discov Today 2003 Mar. 15; 8(6):259-66; Sehgal A, Delivering peptides and proteins to tumors, Drug Discov. Today 8(14):619 [2003]; Koning G A, Storm G, Targeted drug delivery systems for the intracellular delivery of macromolecular drugs, Drug Discov Today 2003 Jun. 1; 8(11):482-3). Such vectors molecules include so-called protein transduction domains (PTDs), which are derived from various viruses or from Drosophila antennapedia. Of special interest for application in HIV disease are HIV Tat and its derivatives which act as PTDs (e.g., Schwarze, S. R., et al., In vivo protein transduction: delivery of a biologically active protein into the mouse, Science 285:1569-72 [1999]).
Anti-HIV drugs have been encapsulated in the aqueous core of immunoliposomes, which include on their external surfaces antigen-specific targeting ligands (e.g., Bergeron, M G. et al., Targeting of infectious agents bearing host cell proteins, WO 00/66173 A3; Bergeron, M G. et al., Liposomes encapsulating antiviral drugs, U.S. Pat. No. 5,773,027; Bergeron, M G. et al., Liposome formulations for treatment of viral diseases, WO 96/10399 A1; Gagne J F et al., Targeted delivery of indinavir to HIV-1 primary reservoirs with immunoliposomes, Biochim Biophys Acta 1558(2):198-210 [2002]; Dufresne I et al., Targeting lymph nodes with liposomes bearing anti-HLA-DR Fab′ fragments, Biochim Biophys Acta 1421(2):284-94 [1999]; Bestman-Smith J et al., Sterically stabilized liposomes bearing anti-HLA-DR antibodies for targeting the primary cellular reservoirs of HIV-1 Biochim Biophys Acta 1468(1-2):161-74 [2000]; Bestman-Smith J et al., Targeting cell-free HIV and virally-infected cells with anti-HLA-DR immunoliposomes containing amphotericin B, AIDS 10; 14(16):2457-65 [2000]).
There are many examples of antibody-targeted liposomes in animal models. Currently, there is also at least one antibody-targeted liposome, termed DOXIL, evaluated clinically. By employing a single-chain antibody that had been raised against ITER2/neu, it is targeted to certain types of breast cancer. Developed by Papahadjopoulos and colleagues at UCSF, this antibody-mediated targeting variant is currently being evaluated in clinical trials at the National Cancer Institute (e.g., Park J W, Hong K, Kirpotin D B, Colbem G, Shalaby R, Baselga J, Shao Y, Nielsen U B, Marks J D, Moore D, Papahadjopoulos D, Benz C C, Anti-HER2 Immunoliposomes: enhanced efficacy attributable to targeted delivery, Clin Cancer Res. 2002 April; 8(4):1172-81 [2002]).
Attempts at active targeting of lymphoid cell populations with liposomes have met with some degree of success. Bestman-Smith et al. (2000) reported that after subcutaneous injection of immunoliposomes bearing anti-HLA-DR Fab′ fragments into mice, there was accumulation of the immunoliposomes in lymphoid tissues (Bestman-Smith J et al., Targeting cell-free HIV and virally-infected cells with anti-HLA-DR immunoliposomes containing amphotericin B, AIDS 10; 14(16):2457-65 [2000]). Gagne J F et al. [2002] reported that subcutaneous injections of immunoliposome-encapsulated anti-HIV drugs resulted in an accumulation of the drug in lymph nodes of injected mice with relatively low toxicity, compared to administration of the free drug; there was no significant difference reported in the ability of anti-HLA-DR-targeted immunoliposomes containing indinavir to inhibit HIV-1 replication in infected PMI cells, compared to free indinavir or non-targeted liposomal-indinavir complexes. Copland et al. targeted the mannose receptors of monocyte-derived dendritic cells (Mo-DCs) and reported that mannosylated liposomes were preferentially bound and taken up by Mo-DCs at 37° C., compared to non-mannosylated neutral liposomes and negatively charged liposomes (Copland, M J et al., Liposomal delivery of antigen to human dendritic cells, Vaccine 21:883-90 [2003]).
The present invention provides a liposomal delivery system that facilitates the targeting of active agents, such as drugs, immunomodulators, lectins or other plant-derived substances specifically to myeloid cell populations of interest. The present invention therefore addresses, inter alia, the need to target the reservoirs of HIV, hepatitis C virus (HCV) in myeloid cells, particularly dendritic cells and macrophages, as well as follicular dendritic cells of myeloid origin, of persons infected with HIV and those suffering from AIDS, or persons infected or co-infected with HCV and those suffering from HCV-dependent pathologic alterations of the liver. In addition, the present invention may allow for indirect targeting of lymphoid cells, particularly T cells, upon their physical interaction with myeloid cells. Moreover, the present invention may allow for the specific elimination, or down-modulation, of malignant tumor cells or immune cells mediating autoimmunity; the enhancement of DC-dependent autologous tumor immunization; the therapeutic down-regulation of autoimmune diseases; or the DC-tropic stimulation of specific adaptive immunity (both in terms of vaccination or treatment) against common pathogens, or pathogens potentially employed as agents of bioterrorism, for which there currently exists no efficient protection. The present invention may also allow for biotechnological advancement, such as, inter alia, by targeting DCs for increasing the production of monoclonal antibodies, or by allowing for the production of such immunoglobulins that cannot be induced in the absence of inductive liposomal DC targeting.